A scalable process for the chemical recycling of PET using ionic organocatalysts

A small pile of plastic waste, including bottles, straws and wrapping.

Professor Joe Wood of the School of Chemical Engineering has teamed up with Professor Andrew Dove of the School of Chemistry to study the chemical recycling of polyethylene terephthalate (PET), with the award of a new grant of £1.17 million from EPSRC.

There is an urgent need to devise processes for recycling plastics, with an estimated total of 8,300 million metric tonnes of plastics produced to date, of which less than 10% have been recycled overall. The end fate of polymers can include landfill, burning which contributes to CO2 production, global warming, and discarding into the environment, including rivers and oceans. Of the materials which are recycled, mechanical or thermal recycling techniques typically produce a lower grade of polymer which can be used in applications such as clothing, insulation, garden and road furniture for example, and also has inferior properties (e.g. colour and mechanical specification) and value compared with virgin polymers. Chemical recycling has the advantage of breaking down the polymer to produce virgin monomer, which can be recycled to new products as part of the Circular Economy.

The work will build on earlier studies of both groups, including a previous project on chemical recycling of polylactic acid in Chemical Engineering. However, PET is selected as the principal polymer for depolymerisation studies in this project, owing to it being widely used, with typical applications in clothing, bottles and packaging. The currently low recycling rates (30 % US – 52 % EU), together with the high value of virgin PET resin (£1084/tonne) and large worldwide demand (~23.5 million tonnes), make a strong economic case for chemical recycling to produce the virgin polymer, rather than mechanical or thermal recycling to a lower grade product.

Chemical recycling of PET can be achieved by reacting the shredded polymer with an alcohol, with the reaction accelerated by a catalyst such as ionic organocatalysts being developed by Professor Dove’s group in Chemistry. Challenges to be addressed in Chemistry include studies of the effect of polymer additives and food contaminants in real wastes such as PET meal trays, upon the depolymerisation, understanding how the catalyst/process can be made resilient to these issues and looking at immobilisation of the catalyst upon a support to facilitate recycling.

Key considerations in Chemical Engineering will be to fully understand reaction kinetics, developing a continuous flow rig to carry out the reaction, and devising strategies for product recovery based on membrane separations and crystallisation.

We have engaged Project Partners from across the recycling, polymer production and academic sectors to advise on and engage with our project. We are currently recruiting a team of postdoctoral researchers and PhD students to work with us and are looking forward to getting started on this exciting project.